EFFECT OF HEN AGE, BODY-WEIGHT, AND AGE AT PHOTOSTIMULATION - 2 - EMBRYONIC CHARACTERISTICS OF COMMERCIAL TURKEYS

Turkey hens from two BW groups (which averaged 11.8 and 12.9 kg, Norma l and Heavy, respectively) were photostimulated at either 29 or 31 wk of age to determine how changes in egg weight and egg component weight s with hen age affect subsequent embryonic growth and yolk sac lipid m obilization. At 2-wk intervals during the first 10 wk of lay, all eggs were collected, individually weighed, and incubated. A subsample of e ggs from each photostimulation (PS) age and BW group were randomly sel ected for yolk and albumen weight determinations and embryo weight, li ver weight, and yolk sac measurements at 21 and 25 d of incubation. Yo lk and yolk sac lipid measurements were done on similar sized eggs sel ected at 4 to 6 and 12 to 14 wk after PS. Yolk-free embryo weight, liv er weight, and yolk sac weight at 21 and 25 d of incubation increased during the first 10 wk of lay. Neither hen age nor BW at PS had any co nsistent effects on yolk-free embryo weight, liver weight, or yolk-sac weight. When similar-sized eggs (80 to 85 g) were selected for analys es, yolk lipid content did not change with hen production age. The Lip id content of the yolk sac was 0.97 g greater in 21-d embryos from hen s 12 to 14 wk after PS than from hens 4 to 6 wk after PS. Differences in yolk sac residual lipid and lipid subclass characteristics were not evident after 25 d of incubation. In conclusion, hen BW at PS or age at PS had minimal affects on embryonic growth during the last week of incubation, and most differences in embryonic growth were attributed t o differences in yolk sac lipid mobilization between hen production ag es independent of egg size.